This invention relates to methods for data communications, and more particularly relates to a method for establishing and maintaining an optical, open-air communications link.
An emerging technology is that of a low cost, high bandwidth, wireless optical data communications system. Such systems utilize a transmitter and receiver, with each transmitter and optionally the receiver having a rotatable micro-mirror and light source, such as a laser, and are used to communicate data on a path-to-sight basis. Many optical wireless systems do not have any feedback method, which requires manual alignment using telescopes precisely aligned to the axis of the outgoing laser beam. To account for system vibrations and mis-alignment, the beam is often slightly mis-collimated, which eases the alignment tolerance. An example of this is in the Terralink 1000X (Astroterra), which has an output divergence of 2.5 mrad, which allows a mis-alignment of 1 mrad.
There is a need for an efficient and effective method for establishing and maintaining the actual link when using such systems.
In accordance with the present invention a method is provided for controlling an optical, path-to-sight link, the optical link including a source of light having a beam of light, a controllable beam steering device to permit steering the light beam, the beam steering device being controllable by predetermined control signals. The method includes the following steps. The beam steering device is controlled so as to scan the beam of light in a first predetermined pattern. First detection data is received from a remote receiver including a light detector, the detection data corresponding to the detected intensity and/or time when the scanned beam of light is detected by the light detector. Responsive to the first detection data, a first beam direction is determined for data communication from the link to the receiver. The beam steering device is controlled to maintain a communications beam direction corresponding to the first beam direction. The beam of light is modulated with electronic signals.
As used herein, the term path-to-sight is intended to mean an unobstructed optical path generally through the ether, as contrasted with through an optic fiber, which path can include reflections.
These and other features of the invention will be apparent to those skilled in the art from the following detailed description of the invention, taken together with the accompanying drawings.